1. Field of the Invention
The present invention relates to a lens drive apparatus in an optical pickup and a method of producing the same.
2. Description of the Prior Art
An optical pickup is provided for converging beams of light into a spot on a recording track arranged on the data recording surface of a recording disk which serves as a data recording medium to read data from the recording track by means of change in the reflected light. For correct convergence of the light beams on the recording track to be retrieved, the pickup allows its objective lens for beam convergence to move a minimal distance in the direction of the optical axis in the focus servo action to compensate for surface deviation caused by the deflection of a recording disk. Also, the objective lens is arranged to move a minimal distance at a right angle to the recording track in the tracking servo action for correct tracing of the light spot along the recording track regardless of eccentricity of the recording track.
Such a conventional optical pickup provided with a lens drive apparatus for servo drive action of the objective lens is shown at its primary section in FIGS. 1 and 2.
As shown in FIG. 1, the optical pickup has a hollow pickup body 141 and an actuator base 142 fixedly installed in the pickup body 141. The pickup body 141 and the actuator base 142 constitute in combination a base section of the optical pickup. The optical pickup is arranged for linear movement along a guide mechanism, not shown, to scan the data recording surface of a disk 143 which is placed on a turn table, not shown, for rotating movement. More specifically, the guide mechanism is a linear guide shaft with which the pickup body 141 is slidably engaged. The optical pickup is driven by a pickup drive means (not shown).
The pickup body 141 contains optical devices for performing a substantial task of the pickup including a semiconductor laser 144 serving as a light emitter means for emission of light beam and a prism 145 for reflecting the light beam at a right angle to run towards an objective lens 147. The light beam from the semiconductor laser 144 is focused by the objective lens 147 to a spot of light on the data recording surface of the disk.
The objective lens 147 is mounted to the uppermost end of a lens holder 148 of cylindrical shape. As best shown in FIG. 2, the lens holder 148 has a focusing coil 150 wound on the circumferential surface thereof so that the center axis of the focusing coil 150 comes in parallel to the optical axis of the objective lens 147. The focusing coil 150 is coupled at outer end to a plurality, e.g. four, of tracking coils 151 of which center axes extend at right angles to the optical axis of the objective lens 147. In more particular, each tracking coil 151 wound into an annular shape is attached to the focusing coil 150. A movable optical system consisted of the objective lens 147 and the lens holder 148 is supported at one end by two pairs or four of elongated suspension resilient members 153 which are arranged parallel to each other and extend at right angles to the optical axis of the objective lens 147 and along a first direction denoted by X of FIG. 2. FIG. 2 illustrates three of the four resilient members 153. Each resilient member 153 is mounted at one end to an upwardly extending upright portion 142a of the actuator base 142 in cantilever arrangement. The actuator base 142 also has a through opening 142c therein across which the optical path extends. The resilient member 153 is formed of e.g. a spring steel material for having resiliency. Accordingly, the movable optical system consisted of the objective lens 147 and the lens holder 148 can be moved in two directions; the direction of the optical axis of the objective lens (denoted by F in FIG. 2) and a second direction (denoted by T) designated at right angles to the optical axis of the objective lens 147 and to the first direction (denoted by X). The optical axis of the objective lens 147 extends in a focusing direction designated vertical to the data recording surface of the disk. Hence, the second direction is equal to a tracking direction which extends at a right angle to the recording track of the data recording surface.
The focusing coil 150 and the tracking coils 151 are arranged to be in a magnetic gap of a magnetic circuit which comprises a magnet 155 and a yoke 156. The magnetic gap yields a parallel magnetic flux extending at a right angle to both the coils 150 and 151. Hence, when the coils 150 and 151 are energized with given currents respectively, they produce drive forces to move the movable optical system in the F and/or T directions.
The procedure of assembling the lens drive apparatus of the conventional optical pickup will be explained referring to FIG. 3.
As shown, the lens drive apparatus is assembled using a specific tooling 158. The tooling 158 comprises a support 158a of planar form for supporting the actuator base 142 and an integrally formed extension 158b extending upwardly from one end of the support 158a in parallel with the upright 142a of the actuator base 142. The support 158a has at center an upwardly extending pillar 158c. Also, a small pillar 158d is coaxially mounted to the uppermost of the center pillar 158c, thus projecting upwardly. In assembly, the actuator base 142 is first loaded onto the tooling 158 with its opening 142c accepting the center pillar 158c. The upright 142a of the actuator base 142 is then tightened by a screw 160 to the extension 158b of the tooling 158. The actuator base 142 carries the magnets 155 and the yokes 156 installed therein. Then, the lens holder 148 is attached to the top of the center pillar 158c. The lens holder 148 carries the focusing coil 150 and the tracking coils 151 assembled preliminarily while the objective lens 147 remains unloaded at the time. The lens holder 148 is tightened by a screw 161 to the tooling 158 with its optical path center opening 148a accepting the small pillar 158d. As the result, the actuator base 142 and the lens holder 148 both are fixedly mounted to the tooling 158 and their relative positioning is completed. Then, the four resilient members 153 shown in FIG. 2 are loaded by an operator. More particularly, the four resilient members 153 are bonded one by one between the upright 142a of the actuator base 142 and the lens holder 148 by application of an adhesive. After bonding the resilient members 153, the two screws 160 and 161 are loosened and an assembled unit is dismounted from the tooling 158. Then, other assembly steps including the mounting of the objective lens 147 to the lens holder 148 will follow.
As understood, the loading and bonding of the four resilient members 153 which are small in size requires the operator to conduct a troublesome and skilled task in the procedure of assembling the conventional lens drive apparatus. Simplification of the task has thus been desired. Also, it is technically difficult during the foregoing action to increase accuracy in the positioning of such components and thus, dislocation or misassignment in the loading and bonding action will be unavoidable. Hence, the task becomes the first thing to be tackled in order to minimize defective optical pickup products.